This invention relates generally to a method for inspecting and permanently recording contact patterns on large reduction gears and more particularly to a method for systematically recording loaded running tooth contact patterns on large gears, such as navy and marine main propulsion reduction gears.
In high torque precision gearing, such as used in reduction gear sets for navy and marine propulsion, proper alignment of the gears with uniform contact along the flanks of the meshing gear teeth is paramount in insuring long life of the gears, as well as quiet and smooth operation. High torque precision gears are more generally furnished with double helical teeth to reduce noise and vibration. The customary procedure for establishing uniform tooth contact across the gear face has been to adjust the bearings that support the gears in the gear casing. Assuming that the gear teeth are perfectly matched, as to helix lead angle and gear modification, uniform tooth contact can then be achieved if the axes of the two gears are both parallel and co-planar.
In the case of navy and marine reduction gears in particular, there are usually two reductions from the input to the output shaft by way of a pair of intermediate shafts. Each of the meshing gear sets are of the "herringbone" or double helical type. Although the gears may be perfectly aligned in the factory and carried in a large casing housing, inevitably misalignment can occur under load in a propulsion gear unit. It is necessary to load (operate) and then inspect the loaded running tooth contact patterns and to make adjustments in the bearings in order to re-establish uniform tooth contact across the gear face.
The customary procedure in the prior art is to coat one set of meshing teeth with a substance to provide a visual indication of tooth wear, and then to run the gears under load. Subsequently the visual inspection is made and the contact patterns are recorded by making a sketch of the contact areas of representative gear teeth. The major problem with this method is that the quality and accuracy of the sketch will vary greatly with the artistic ability of the inspector. In addition it is easy for the inspector to make the mistake of reversing the ahead and astern tooth flank sketches or reversing the right hand and left hand helices. In addition, viewing of the contacts is complicated by the lack of light inside the gear casing and by the reflections caused by any exterior light source.
It would be desirable to make a permanent, precise and objective record of loaded running tooth contacts in order to allow accurate decisions to be made regarding the bearing adjustments necessary to achieve optimum tooth contact under full design load. It is also important to know of alignment/tooth contact changes that may take place by comparing the permanent record to future inspections.
Accordingly, one object of the present invention is to provide an improved method of permanently recording loaded running tooth patterns in large reduction gears.
Another object of the invention is to provide a more accurate method by way of video image recording the running tooth patterns which also removes the subjectivity which is inherent in individual hand sketch recording.